what happened to incoming mails when we planned shutdown for mail server ?

Hi,

I have one query ...

When we do planned shutdown for mail server..then ofcourse people wont able to login to mail server..but when external doamin try to send mails to this domain ( as they are not aware about the downtime) then MTA of their server will keep trying to send mails and it will be in queue ....and once they get connection to this domain when server gets up then it will deliver the mail which is in queue....

Is it correct ??? if not then please correct me...

If above explanation is correct then what is the standard duration for mails to stay in MTA queue..means how long they keep trying to reach tht mail server which is down ??

And for my zimbra server where can i find out the setting for this duration..?

The default behaviour of pretty much every SMTP server is to queue messages for up to 1 week before bouncing the message back to the sender as "undeliverable". They will keep trying, waiting longer and longer between tries.

For Zimbra, this is handled by Postfix (the SMTP server) and the settings will be stored either in the Postfix config (main.cf.in) or somewhere in the Zimbra registry.

And, if you do use a secondary/backup MX server, be sure to implement the same (or better) anti-virus and anti-spam checking on it as on the primary MX server. Or, configure the primary MX server to not trust the backup MX and to run all messages through the av/as.

A lot of spammers search out secondary MX servers and use those to send messages as the defenses tend to lag behind on them.